The rumen or forestomach is an organ found in the digestive tract of certain herbivorous mammals prior to the gastric stomach and within which the digestion and formentation of plant material occurs through the activity of special microbial populations. A group of which some are found amongst such microbial populations are the Archae.
The Archae are a diverse group with regard to their physiology and include the methanogens, halophiles and thermacidophiles. They are related through ribosomal RNA sequences that differ drastically from those of other procaryotes. Because of the anaerobic conditions in the rumen only those Archae that are obligate anaerobes are found therein. One member of the Archae found in the rumen, the methanogens are able to produce methane in symbiosis with other rumen microorganisms. For example, H.sub.2 and CO.sub.2 are common end products and these may subsequently be used by the methanogens in the production of methane.
It has been recognised for some time, see e.g. Baxter, K. L. (1962) `The Energy Metabolism of ruminants` (Hutchinson, London), that rumen methanogenesis can result in a loss of energy available to an animal, a loss equivalent to possibly 10% of an animal's gross energy intake. To reduce this loss several procedures for the inhibition of methanogenesis in the rumen have been investigated over the years. These procedures include the use of feed additives such as long-chain unsaturated fatty acids and the administration of ionophoric drugs to inhibit the production of H.sub.2. Varying degrees of inhibition of methanogenesis have been demonstrated although in no case has it been clearly established that the overall result was economically favourable. Furthermore, irrespective of any technical inadequacies, the concept of constant administration of feed additives and drugs to meat-producing animals is increasingly regarded with disfavour by meat consumers.